Drat! I accidentally deleted an email from a Greek pastry student that contained an interesting question. That is: why will cold milk foam but warm milk won’t? The answer is butterfat again, even though milk doesn’t have near enough of it to form a foam that has any long-term stability. It’s still fat crystals (along with some miscellaneous proteins) that are helping to reinforce the bubble walls…temporarily. But butterfat crystals can only form in cool temperatures, so warm milk won’t foam nearly as well.
The worst thing about losing this email is that this particular Greek student offered to share some good recipes with me. So please do write back…because I’m greedy!